The House isn't very popular these days, so why would anyone want to return there after a 20-year hiatus? The answer — if there is one — is just one reason why the crowded primary for this suburban Philadelphia, strong Democratic district is so fascinating.

Former Rep. Marjorie Margolies, D-Pa., is waging a comeback bid for the 13th District nearly tw0 decades after she supported President Bill Clinton's budget and famously lost re-election in 1994. The 71-year-old is back with a vengeance and strong political connections: Her son is married to Chelsea Clinton. Her primary opposition only makes this open-seat race to succeed Rep. Allyson Y. Schwartz, D-Pa., who is running for governor, more interesting. There's state Sen. Daylin Leach, a liberal lion who supports marijuana legalization, state Rep. Brendan Boyle, who boasts support from Rep. Bob Brady, D-Pa., and University of Pennsylvania medical professor Valerie Arkoosh, a Schwartz ally.

Margolies' early polling shows her with a big advantage, but that's more likely a demonstration of her high name identification in the district. There's still a great deal of time to air television ads before the May 20 primary.

Most importantly, the winner stands to reveal something something about the future of the Democratic Party in this crucial southeastern corner of the state. The party is at a crossroads statewide, with more socially conservative Reagan Democrats facing off with a more liberal, pro-business wing. Margolies campaigned as a moderate in 1992, but the 13th District has changed drastically and now leans much further to the left.

What's more, this district includes the pricey Philadelphia media market. Whoever wins this primary will probably hold this seat for as long as he or she wants to keep it, stockpiling cash from Philadelphia's tony suburbs. Eventually, they will probably be in a strong position, like Schwartz, to run statewide some day.

The race is rated Safe Democrat by Rothenberg Political Report/Roll Call.

Editor’s note: Not all congressional races are created equal, and Roll Call’s politics desk admits to playing favorites. So in the spirit of the holidays, these are a few of our favorite things (races) to cover this cycle. We’re shining a spotlight on our 12 most fascinating races through the new year — in no particular order. Happy holidays from @RollCallPols!